The objective of this project is to systematically collect and distribute high quality biopsy and/or freshly autopsied tissues from "unaffected" (control) individuals and from patients who had been diagnosed to have a known or unknown forms of mental retardation, developmental disabilities, or infants who die of sudden infant death syndrome (SIDS). Among the conditions from whom specimens will be obtained include those with chromosome defects, mitochondrial myoencephalopathies, phenylketonuria and other aminoacidopathies, organic acidurias, maternal PKU, Rett syndrome, leukodystrophies, lysosomal storage disorders, dyslexia, autism, and other neurodevelopmental disorders. The repository will serve as a research resource for qualified investigators to support and facilitate research that will lead to an improved understanding of the etiology, pathology, pathogenesis, and clinical-pathological correlation of conditions that are associated with SIDS, mental retardation, learning and behavioral deficits. Since the repository will collect normal and abnormal brains at various prenatal and postnatal stages of development, it can also provide material for the longitudinal studies of brain development and its malformations.